To smooth an inside curve without flattening its shoulders, support the abrasive on a backer that fits the hollow. Then use light witness marks to check contact and stop when the machining scratches disappear. This is a hand-sanding method for an already shaped curve, such as an apron cutout, handle or cove—not a way to correct a badly cut outline.
1. Preserve a reference before you start
Keep the template or trace the intended curve onto card. For a curved edge, compare both faces of the workpiece with this outline. Check that the edge is reasonably square to the faces where the design requires it. If the saw left a large hump, remove it with an appropriate shaping tool first. Fine paper is a slow way to do that job, and impatience usually means uneven pressure.
Secure the part with padded clamps so the entire sanding stroke is clear of the bench. Do not sand an unsupported narrow arm that flexes under your hand; support it close to the worked area. Vacuum dust as you go and use suitable dust protection. Brush the surface clean for inspection instead of blowing dust into the room.
2. Choose a backer for the actual curve
A dowel works for a small hollow if the paper-wrapped diameter fits. A commercial rubber contour grip is useful for repeatable coves. For a broad arc, a shaped cork or firm foam block offers better support than fingertips. Woodcraft describes making a complementary block from the workpiece offcut or a traced curve; account for the added thickness of the abrasive when checking the fit.
| Shape | Useful backer | What to avoid |
|---|---|---|
| Narrow, constant-radius cove | Fitted dowel or rounded contour grip | An oversized dowel that only rubs the lips |
| Broad circular hollow | Shaped cork or firm foam block | A flat block bridging the middle |
| Curve with changing radius | Several smaller fitted backers, worked in sections | Forcing one large radius through every section |
| Curve beside a crisp shoulder | Narrow backer that stays within the hollow | Soft paper rolling over the boundary |
Attach the paper securely, keeping overlaps and seams away from the cutting face. Write the grit on the block so you do not accidentally return to coarse paper. Make the block wide enough to support the surface you are sanding, but not so bulky that it cannot follow the changing curve.
3. Prove contact before increasing pressure
Draw several faint pencil strokes across the area, then make a few easy passes. Clean off the dust and inspect the marks. If only the ends disappear, the backer is bridging the hollow. If one small stripe disappears in the middle while adjacent marks remain, contact is too concentrated. Adjust the backer or use shorter sections; extra pressure does not fix a poor fit.
4. Work through the scratches, not past the shape
Start with the finest grit that removes the existing tool marks at a reasonable pace. On a fairly clean cut, 120 followed by 150 and 180 is a useful trial sequence, not a rule for every wood or finish. Coarse saw damage may need shaping first. Follow the finish manufacturer's preparation directions for the final grit.
Use light overlapping strokes along the grain where the geometry permits. Keep the backer seated rather than rocking it around its edges. For a curved board edge, stop regularly to compare both face outlines; sanding at a tilt can make one face smaller than the other. Change tired abrasive instead of bearing down harder.
Remove the scratches from one grit before changing to the next. Vacuum or brush the block and wood between stages so loose coarse particles do not add new scratches. Finish adjoining flats and curved areas to a compatible preparation; an unsanded patch in the hollow can show clearly after stain.
5. Check with light, touch and the template
Move a low light across the curve and look for repeating ridges or shiny bands. Feel along it with a clean hand, then compare it to the saved outline. A smooth surface can still be the wrong shape. Stop when machining marks are gone and the profile is intact; repeatedly rubbing one visible spot risks making it a dip.
If the next step is staining, use a matching offcut to check the result. Exposed end grain in a curved cut can absorb differently; preparing end grain for stain addresses that color problem separately.
Sources
Woodcraft: Smoothing Curves; Lee Valley: Contour Sanding Grips; WOOD: Keys to Successful Hand-Sanding.
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